Peroxydisulfate Activation and Singlet Oxygen Generation by Oxygen Vacancy for Degradation of Contaminants

Origin of the Excellent Activity and Selectivity of a Single-Atom Copper Catalyst with Unsaturated Cu-N2 Sites via Peroxydisulfate Activation: Cu(III) as a Dominant Oxidizing Species

As an efficient active oxidant for the selective degradation of pollutants in wastewater, the high-valent copper species Cu(III) with persulfate activation has attracted substantial attention in some Cu-based catalysts. However, the systematic study of a catalyst structure and mechanism about Cu(III) with peroxydisulfate (PDS) activation is challenging owing to the coexistence of multiple Cu species and the structural symmetry of PDS. Herein, we anchored a Cu atom with two pyridinic N atoms to synthesize a single-atom Cu catalyst (Cu_SA-NC). Experimental characterizations and theoretical calculations complemented each other well because of the uniform atomic active sites. The single-atom Cu was identified as the active site, and the unsaturated Cu-N₂ configuration was more conductive to PDS activation than the saturated Cu-N₄ configuration. Benefiting from the generation of Cu(III), Cu_SA-NC exhibited an obvious selective and anti-interference performance for pollutant degradation in a complex matrix. The superior catalytic activity of Cu_SA-NC compared with that of other reported Cu-based catalysts and good durability in a continuous-flow experiment further revealed the potential of Cu_SA-NC for practical applications. This work strongly deepens the understanding of the generation of Cu(III) in a single-atom Cu catalyst with unsaturated Cu-N₂ sites under PDS activation and develops an efficient approach for actual water purification.

Oxygen Vacancy-Mediated CuCoFe/Tartrate-LDH Catalyst Directly Activates Oxygen to Produce Superoxide Radicals: Transformation of Active Species and Implication for Nitrobenzene Degradation

Oxygen vacancies play a vital role in the catalytic activity of layered double hydroxide (LDH) catalysts in wastewater treatment. However, the mechanism of oxygen vacancy-mediated LDH-activated oxygen to produce reactive oxygen species (ROS) still lacks a reasonable explanation. In this work, a tartrate-modified CuCoFe-LDH (CuCoFe/Tar-LDH) with abundant oxygen vacancies was designed, which can efficiently degrade nitrobenzene (NB) under room conditions. The technical energy consumption is 0.011 kW h L^-1. According to the characterization and calculation results, it is proposed that oxygen vacancies are formed because of the oxygen deficiency which is caused by the reduction of the energy between the metal ion and oxygen, and the metal ion transitions to a lower state. Compared with CuCoFe-LDH, the oxygen vacancy formation energy of CuCoFe/Tar-LDH decreased from 1.98 to 1.13 eV. The O₂ bond length adsorbed on the oxygen vacancy is 1.27 Å, close to the theoretical length of superoxide radicals (^•O₂^-) (1.26 Å). Radical trapping experiments and electron spin-resonance spectroscopy spectrum prove that ^•O₂^- is an important precursor of ^•OH. This work is dedicated to the in-depth exploration of the oxygen vacancy-mediated CuCoFe/Tar-LDH catalyst activation mechanism for molecular oxygen and the conversion relationship between ROS.

Monodispersed CuO nanoparticles supported on mineral substrates for groundwater remediation via a nonradical pathway

Nonradical oxidation based on singlet oxygen (¹O₂) has attracted great interest in groundwater remediation due to the selective oxidation property and good resistance to background constituents. Herein, recoverable CuO nanoparticles (NPs) supported on mineral substrates (SiO₂) were prepared by calcination of surface-coated metal-plant phenolic networks and explored for peroxymonosulfate (PMS) activation to generate ¹O₂ for degrading organic pollutants in groundwater. CuO NPs with a close particle size (40 nm) were spatially monodispersed on SiO₂ substrates, allowing highly exposure of active sites and consequently leading to outstanding catalytic performance. Efficient removal of various organic pollutants was obtained by the supported CuO NPs/PMS system under wide operation conditions, e.g., working pH, background anions and natural organic matters. Chemical scavenging experiments, electron paramagnetic resonance tests, furfuryl alcohol decay and solvent dependency experiments confirmed the formation of ¹O₂ and its dominant role in pollutants removal. In situ characterization with ATR-FTIR and Raman spectroscopy and computational calculation revealed that a redox cycle of surface Cu(II)-Cu(III)-Cu(II) was responsible for the generation of ¹O₂. The feasibility of the supported CuO NPs/PMS for actual groundwater remediation was evaluated via a flow-through test in a fixed-bed column, which manifested long-term durability, high mineralization ratio and low metal ion leaching.

Construction of Li/K dopants and cyano defects in graphitic carbon nitride for highly efficient peroxymonosulfate activation towards organic contaminants degradation

As an emerging peroxymonosulfate (PMS) activation catalyst, graphitic carbon nitride (g-C₃N₄) is non-toxic and eco-friendly, while its poor catalytic performance hinders the application of pristine g-C₃N₄. Herein, a simple LiCl/KCl molten salts-assisted thermal polymerization method was adopted to promote the photocatalytic performance of g-C₃N₄. With the insertion of Li/K dopants and the introduction of surface cyano defects, the modified catalyst exhibited greatly enhanced ability on PMS activation towards acetaminophen removal, observing a 13 times higher rate constant than pristine g-C₃N₄ (k = 0.0435 min^-1 vs. 0.0033 min^-1). The main reactive oxygen species for pollutant degradation were identified as sulfate radicals and singlet oxygen. The wavefunction analysis at excited states based on density functional theory suggests that the introduction of cyano defects greatly promotes the separation of photo-generated electron-hole pairs, thereby achieving higher photocatalytic efficiency. In addition, the doping of Li/K significantly enhances the interaction between PMS and the catalyst surface, and orients the electron transfer from PMS to catalyst to generate non-radical species singlet oxygen, which improves the catalyst resistance to anions-containing water matrices.

Peroxymonosulfate Activation on Synergistically Enhanced Single-Atom Co/Co@C for Boosted Chemiluminescence of Tris(bipyridine) Ruthenium(II) Derivative

Tris(bipyridine) ruthenium(II)-based luminophores have been well developed in the area of electrochemiluminescence, while their applications in chemiluminescence (CL) are rarely studied due to the poor luminous efficiency and complicated CL reaction. Herein, a novel tris(bipyridine) ruthenium(II)-based ternary CL system is proposed by introducing cobalt single atoms integrated with graphene-encapsulated cobalt nanoparticles (Co SAs/Co@C) and peroxymonosulfate (PMS) as advanced coreaction accelerator and promising coreactant, respectively. On the basis of the experimental results and density functional theory calculations, it is concluded that Co@C can synergistically modulate the adsorption behavior of PMS on Co SAs and then efficiently activate PMS to produce massive singlet oxygen for remarkable CL emission. Under the optimum conditions, the as-prepared CL biosensor exhibits a good linear range, excellent sensitivity, and selectivity, holding great potential for the practical detection of prostate-specific antigen in human serum.

Photoelectrocatalytic mechanism of PEDOT modified filtration membrane

The generation of free radicals is the key to the photocatalytic efficiency. In this study, the degradation mechanism of photoelectrocatalysis (PEC) membrane could be adequately explained by exploring the generation pathway of different free radicals. The PEC membrane was prepared by gas phase polymerization of poly (3, 4-ethylene dioxythiophene) (PEDOT) on non-woven fabric, industrial filter cloth, ceramic membrane and polyvinylidene fluoride (PVDF) membrane, respectively. Three-dimensional fluorescence test showed that the optimal degradation of mixed or monomer contamination (bovine serum protein, sodium humate, and sodium alginate) was achieved by modified ceramic membrane under PEC condition. As for self-cleaning experiment, the membrane resistance decreased 65.7% when the reaction conditions changed from dark to PEC for 30 min. Combined with the characterization results, PEDOT as photocapacitance extended electron lifetime and promoted free radical generation. This system was mainly dependent on superoxide free radicals (0.01 mmol/L) and singlet oxygen (0.10 mmol/L), which came from energy and electron transfer. Oxygen vacancy could adsorb oxygen to produce superoxide radicals, which was further oxidized to singlet oxygen. In addition, the π-electron conjugated system of PEDOT accelerated the hole transfer and the separation of electrons and holes. Also, this study provided a new view of reactive oxygen species generation mechanism from PEDOT modified membrane.

Surface oxygen vacancies formation on Zn2SnO4 for bisphenol-A degradation under visible light: The tuning effect by peroxymonosulfate

Visible light catalysis has been widely coupled with persulfate activation for refractory pollutants removal, while the exact role of persulfate played in such composite system is still questionable. In this work, the relation between peroxymonosulfate (PMS) induced structure change and visible light responsive activity of inverse spinel: i.e., Zn₂SnO₄, was deciphered. Under the visible light illumination (λ> 420nm) PMS addition would endow the composite system with pollutant removal performance. Batch test revealed that 60% of bisphenol-A (5 mg L^-1) was mineralized within 3 h reaction time, by dosing 0.81 mM PMS and 0.1 g L^-1 catalyst. The above oxidative system was also effective for other refractory pollutants elimination. Further analysis indicated that PMS could reduce the band gap of spinel from 2.75 to 2.52 eV and thereby enabling its visible light activity. Photogenerated h⁺ induced •OH and e^- mediated •O₂^- contributed to the pollutant removal while h⁺ played a leading role. Density functional theory revealed that PMS would capture oxygen atom of spinel and induce surface oxygen vacancy defect structure formation. Also, three-oxygen atom coordinated Zn was identified as the possible catalyze site. This work is valuable for deep understanding the exact role of persulfate in photocatalytic system.

Brønsted-acid sites promoted degradation of phthalate esters over MnO2: Mineralization enhancement and aquatic toxicity assessment

Advanced oxidation processes (AOPs) are important technologies for aqueous organics removal. Despite organic pollutants can be degraded via AOPs generally, high mineralization of them is hard to achieve. Herein, we synthesized a manganese oxide nanomaterial (H2-OMS-2) with abundant Brønsted-acid sites via ion-exchange of cryptomelane-type MnO₂ (OMS-2), and tested its catalytic performance for the degradation of phthalate esters via peroxymonosulfate (PMS) activation. About 99% of dimethyl phthalate (DMP) at a concentration of 20 mg/L could be degraded within 90 min and 82% of it could be mineralized within 180 min over 0.6 g/L of catalyst and 1.8 g/L of PMS. The catalyst could activate PMS to generate SO₄^-˙ and ·OH as the dominant reactive oxygen species to reach complete degradation of DMP. Especially, the higher TOC removal rate was obtained due to the rich Brønsted-acid sites and surface oxygen vacancies on the catalyst. Kinetics and mechanism study showed that Mn^II/Mn^III might work as the active sites during the catalytic process with a lower reaction energy barrier of 55.61 kJ/mol. Furthermore, the catalyst could be reused for many times through the regeneration of the catalytic ability. The degradation and TOC removal efficiencies were still above 98% and 65% after seven consecutive cycles, respectively. Finally, H2-OMS-2-catalyzed AOPs significantly reduced the organismal developmental toxicity of the DMP wastewater through the investigation of zebrafish model system. The present work, for the first time, provides an idea for promoting the oxidative degradation and mineralization efficiencies of aqueous organic pollutants by surface acid-modification on the catalysts.

Enhanced photocatalytic efficiency by direct photoexcited electron transfer from pollutants adsorbed on the surface valence band of BiOBr modified with graphitized C

Herein, a novel BiOBr photocatalyst with partial surface modification by graphitized C (BiOBr-C_g) was synthesized through a hydrothermal method with hydrothermal carbonation carbon (HTCC) as a slow-releasing carbon source and characterized by experimental and theoretical methods. BiOBr-C_g exhibited excellent visible-light photocatalytic performance toward various refractory pollutants, such as bisphenol A, ibuprofen, ciprofloxacin, 2,4-dichlorophenoxyacetic acid, and diphenhydramine. The characterization results demonstrate that a strong molecular orbital interaction occurs between graphitized C and BiOBr, resulting in the formation of a new surface valence band on graphitized C. This not only promotes the oxidation of pollutants by surface holes but also reduces the recombination of carriers during the bulk phase transfer process, thereby increasing the number of photogenerated carriers. Intriguingly, the analytical results for degradation intermediates and other characterization techniques demonstrate that the pollutants adsorbed on the graphitized C of BiOBr-C_g can be directly excited through light irradiation and react along the organic radical degradation pathway in addition to pollutant degradation by holes and HO₂^•/O₂^•-.

Facilitating Redox Cycles of Copper Species by Pollutants in Peroxymonosulfate Activation

The redox behavior of metal active sites determines the rate of heterogeneous catalysis in peroxymonosulfate activation. Previous reports focused on the construction of catalysts for accelerating interfacial electron transfer. In this work, a new strategy was proposed for facilitating valence cycles of Cu⁺/Cu²⁺ by using pollutants. The 2.5Cu/CeO₂/PMS system was capable of achieving the efficient removal of pollutants, including tetracycline, oxytetracycline, and rhodamine B, in a wide pH working range. In the presence of tetracycline, a Cu-N bond was formed between the -NH₂ group of tetracycline and the Cu site of the catalyst, showing that the coordination of Cu active sites changed to CuO₄N₁. The charge of CuO₄N₁ active sites rearranged, making it easier to obtain electrons and promote the PMS oxidation, thereby accelerating the reduction of Cu²⁺ to Cu⁺ and PMS activation. The PMS activation system showed excellent sustainability and selectivity for the removal of organic pollutants. This study provides a novel routine to promote peroxymonosulfate activation by utilizing pollutants to accelerate the redox behavior of metal species.

Feasibility of micropollutants removal by solar-activated persulfate: Reactive oxygen species formation and influence on DBPs

As a natural source of visible light and a type of renewable energy, solar energy is extensively used in the field of photochemistry. In this study, solar was employed to activate persulfate (PS) to degrade typical micropollutants. The removal kinetics of aspirin (ASA) and flunixin meglumine (FMME) in the solar/PS system were well fitted by pseudo-first-order models (R² > 0.99). In the system containing 1.0 mM PS activated by solar irradiation at a fluence of 1.14 × 10^-4 E·m^-2·s^-1, 72.6% and 97.5% of ASA and FMME were degraded, and the corresponding kinetic constants were 6.8-9.8 × 10^-2 and 1.6-9.8 × 10^-1 min^-1, respectively. Qualitative and quantitative analyses of the reactive oxygen species (ROS) indicated that sulfate radical (SO₄^·-) played a major role in degradation, with the maximum contributions of 77.7% and 88.8% for the degradation of ASA and FMME, whereas the maximum contributions of hydroxyl radical (·OH) were only 11.6% and 6.5%, respectively. The contributions of singlet oxygen (¹O₂) were less than 15% at pH 5.5, but increased to 25.6% and 45.5% at pH 8.5, respectively. Solar/PS pre-oxidation increased disinfection byproducts (DBPs) (95.8% for trihalomethanes (THMs) and 47.9% for haloacetic acids (HAAs) at pH 7.0) after chlorination in deionized water, and an opposite trend was found in systems coexisting with natural organic matter (NOM). Residual PS after oxidation resulted in a high aquatic toxicity, with an inhibition rate of 18.70% to algae growth. Economic analysis showed that the electrical energy per order values of the system ranged from 23.5 to 86.5 kWh·m^-3·order^-1, indicating that the solar/PS system shows promise for practical applications.

Visible Light-Induced Catalyst-Free Activation of Peroxydisulfate: Pollutant-Dependent Production of Reactive Species

Activation of peroxydisulfate (PDS, S₂O₈^2-) via various catalysts to degrade pollutants in water has been extensively investigated. However, catalyst-free activation of PDS by visible light has been largely ignored. This paper reports effective visible light activation of PDS without any additional catalyst, leading to the degradation of a wide range of organic compounds of high environmental and human health concerns. Importantly, the formation of reactive species is distinctively different in the PDS visible light system with and without pollutants [e.g., atrazine (ATZ)]. In addition to SO₄^•- generated via S₂O₈^2- dissociation under visible light irradiation, O₂^•- and ¹O₂ are also produced in both systems. However, in the absence of ATZ, H₂O₂ and O₂^•- are key intermediates and precursors for ¹O₂, whereas in the presence of ATZ, a different pathway was followed to produce O₂^•- and ¹O₂. Both radical and nonradical processes contribute to the degradation of ATZ in the PDS visible light system. The active role of ¹O₂ in the degradation of ATZ besides SO₄^•- is manifested by the enhanced degradation of contaminants and electron paramagnetic resonance spectroscopy measurements in D₂O.

Nonprecious bimetallic Fe, Mo-embedded N-enriched porous biochar for efficient oxidation of aqueous organic contaminants

Bimetallic Fe- and Mo-embedded N-enriched porous biochar (Fe-Mo@N-BC) is developed and serves as a cost-effective and highly efficient catalyst for mineralization of non-biodegradation organic contaminants. Fe-Mo@N-BC was prepared by pyrolysis of complex Fe/Mo -containing precursors. Transmission electron microscopy and elemental mapping suggested that Fe and Mo are uniformly dispersed in nitrogen-doped biochar with hierarchical mesopores. In comparison to Fe@N-BC and Mo@N-BC, Fe-Mo@N-BC exhibited a superior activity for activating peroxymonosulfate (PMS). The stable activity was ascribed to N-doping and synergistic effect of Fe and Mo species, where both Fe-N_x and Mo-N_x can simultaneously serve as the active sites and N-BC can act as a carrier and an activator as well as an electron mediator. Electron paramagnetic resonance and quenching experiments indicated that HO^•, O₂^•- and ¹O₂ were responsible for organic degradation. The effects of PMS dosage, initial Orange II concentration, temperature, solution pH, coexisting anions and humic acids on organic degradation were also investigated. With the assistance of an external magnet, Fe-Mo@N-BC can be easily separated after reaction and remains stable in the reusability tests. This work demonstrates a feasible strategy towards the fabrication of Fe, Mo-embedded N-enriched porous biochar catalysts for the detoxification of organic contaminants.

Preparation and performance of Novel Ni-doped Iron oxychloride with High singlet oxygen generation

Singlet oxygen with lower oxide electrode potential but higher selective oxidation ability towards specific organic contaminants had been paid great attention. An efficient system with high singlet oxygen generation (over...

Revisiting the Graphitized Nanodiamond-Mediated Activation of Peroxymonosulfate: Singlet Oxygenation versus Electron Transfer

Graphitized nanodiamonds (ND) exhibit outstanding capability in activating peroxymonosulfate (PMS) for the removal of aqueous organic micropollutants (OMPs). However, controversial observation and interpretation regarding the effect of graphitization degree on ND's activity and the role of singlet oxygen (¹O₂) in OMP degradation need to be clarified. Herein, we investigated graphitized ND-mediated PMS activation. Experiments show that the activity of ND increases first and then decreases with the monotonically increased graphitization degree. Further experimental and theoretical studies unveil that the intensified surface graphitization alters the degradation mechanism from singlet oxygenation to an electron-transfer pathway. Moreover, for the first time, we applied a self-constructed, time-resolved phosphorescence detection system to provide direct evidence for ¹O₂ production in the PMS-based system. This work not only elucidates the graphitization degree-dependent activation mechanism of PMS but also provides a reliable detection system for in situ analysis of ¹O₂ in future studies.

Cu-doped Ni-LDH with abundant oxygen vacancies for enhanced methyl 4-hydroxybenzoate degradation via peroxymonosulfate activation: key role of superoxide radicals

Oxygen vacancies (OVs) were introduced into Ni-based layered double hydroxides (LDHs) through Cu doping, and the catalytic performance of the resulting Ni_xCu-LDHs were investigated for peroxymonosulfate (PMS) activation and methyl 4-hydroxybenzoate (MeP) degradation. Compared with that of Ni-LDH, the catalytic performance of Ni_xCu-LDHs were significantly enhanced and increased with increasing OV content in the catalysts, indicating that Cu doping introduced OVs into Ni_xCu-LDHs and greatly improved their catalytic activity with PMS. Quenching experiments and EPR analyses confirmed that oxidation processes dominated by superoxide radicals (O₂^•-) and singlet oxygen (¹O₂), rather than sulfate radicals (SO₄^•-) or hydroxyl radicals (•OH) used by traditional LDH catalysts, were responsible for MeP degradation by Ni₁₅Cu-LDHs. In addition, quenching experiments with different systems showed the fate of reduced SO₄^•-and •OH, and demonstrated that O₂^•- and ¹O₂ concentrations grew with increasing OV content, confirming that the presence of OVs affected the process of PMS activation. Notably, O₂^•- mainly originated from adsorbed oxygen or dissolved oxygen (DO) by acquiring electrons from OVs in Ni₁₅Cu-LDHs, since OVs possess abundant localized electrons. Consequently, an OV-mediated oxidative mechanism was proposed for Ni₁₅Cu-LDHs/PMS. This study provides new clues for enhancing the catalytic performance of LDH catalysts by introducing OVs via metal doping in PMS-based AOPs systems.

Oxygen Vacancy-Induced Nonradical Degradation of Organics: Critical Trigger of Oxygen (O2) in the Fe-Co LDH/Peroxymonosulfate System

Ubiquitous oxygen vacancies (Vo) existing in metallic compounds can activate peroxymonosulfate (PMS) for water treatment. However, under environmental conditions, especially oxygenated surroundings, the interactions between Vo and PMS as well as the organics degradation mechanism are still ambiguous. In this study, we provide a novel insight into the PMS activation mechanism over Vo-containing Fe-Co layered double hydroxide (LDH). Experimental results show that Vo/PMS is capable of selective degradation of organics via a single-electron-transfer nonradical pathway. Moreover, O₂ is firstly demonstrated as the most critical trigger in this system. Mechanistic studies reveal that, with abundant electrons confined in the vacant electron orbitals of Vo, O₂ is thermodynamically enabled to capture electrons from Vo to form O₂^•- under the imprinting effect and start the activation process. Simultaneously, Vo becomes electron-deficient and withdraws the electrons from organics to sustain the electrostatic balance and achieve organics degradation (32% for Bisphenol A without PMS). Different from conventional PMS activation, under the collaboration of kinetics and thermodynamics, PMS is endowed with the ability to donate electrons to Vo as a reductant other than an oxidant to form ¹O₂. In this case, ¹O₂ and O₂^•- act as the indispensable intermediate species to accelerate the circulation of O₂ (as high as 14.3 mg/L) in the micro area around Vo, and promote this nano-confinement electron-recycling process with 67% improvement of Bisphenol A degradation. This study provides a brand-new perspective for the nonradical mechanism of PMS activation over Vo-containing metallic compounds in natural environments.

Facile synthesis of oxygen vacancies enriched α-Fe2O3 for peroxymonosulfate activation: A non-radical process for sulfamethoxazole degradation

Hematite (α-Fe₂O₃) has been commonly used as an eco-friendly catalyst for peroxymonosulfate (PMS) to generate free radicals (SO₄^•- and/or •OH). However, the activation efficiency of PMS relies heavily on the conversion of Fe(III) to Fe(II) that is slow and rate-limiting. In this study, oxygen vacancies enriched α-Fe₂O₃ was prepared from thermally treated goethite (α-FeOOH) and employed as a PMS activator. Systematic characterization demonstrated that α-Fe₂O₃ with most abundant oxygen vacancies could be obtained by heating α-FeOOH at 300 °C. The as-prepared α-Fe₂O₃ exhibited excellent catalytic activity in activation of PMS for oxidation of sulfamethoxazole (SMX, k = 0.04 min^-1). The SMX degradation rate was found to be positively correlated with the concentration of oxygen vacancies. Quenching experiments, EPR, LC/MS and XPS analysis revealed that singlet oxygen (¹O₂) was the predominant reactive oxygen species. The effects of pH, PMS dosage, catalyst loading, temperature, and anions on SMX degradation were comprehensively investigated. Moreover, the plausible degradation pathways of SMX in the α-Fe₂O₃/PMS system were proposed. This work not only provides a valuable insight into the mechanism of PMS activation by α-Fe₂O₃ but also establishes a new strategy for the design of more efficient and practical iron-based catalyst for PMS activation.

Thermal Disproportionation for the Synthesis of Silicon Nanocrystals and Their Photoluminescent Properties

In the past decades, silicon nanocrystals have received vast attention and have been widely studied owing to not only their advantages including nontoxicity, high availability, and abundance but also their unique luminescent properties distinct from bulk silicon. Among the various synthetic methods of silicon nanocrystals, thermal disproportionation of silicon suboxides (often with H as another major composing element) bears the superiorities of unsophisticated equipment requirements, feasible processing conditions, and precise control of nanocrystals size and structure, which guarantee a bright industrial application prospect. In this paper, we summarize the recent progress of thermal disproportionation chemistry for the synthesis of silicon nanocrystals, with the focus on the effects of temperature, Si/O ratio, and the surface groups on the resulting silicon nanocrystals’ structure and their corresponding photoluminescent properties. Moreover, the paradigmatic application scenarios of the photoluminescent silicon nanocrystals synthesized via this method are showcased or envisioned.

Critical review of natural iron-based minerals used as heterogeneous catalysts in peroxide activation processes: Characteristics, applications and mechanisms

Recently, an increasing number of works have been reported about iron-based materials applied as catalysts in peroxide activation processes to degrade pollutants in water. Iron-based catalysts include synthetic and natural iron-based materials. However, some synthetic iron-based materials are difficult to scale up in the practical applications due to high cost and serious secondary environmental pollution. In contrast, natural iron-based minerals are more available and cheaper, and also hold a great promise in peroxide activation processes for pollutant degradation. In this review, we classify different natural iron-based materials into two categories: iron oxide minerals (e.g., magnetite, hematite, and goethite,), and iron sulfide minerals (e.g., pyrite and pyrrhotite,). Their overview applications in peroxide activation processes for pollutant degradation in wastewaters are systematically summarized for the first time. Moreover, the peroxide activation mechanisms induced by natural minerals, and the influences of reaction conditions in different systems are discussed. Finally, the application prospects and existing drawbacks of natural iron-based minerals in the peroxide activation processes for wastewater treatment are proposed. We believe this review can shed light on the application of natural iron-based minerals in peroxide activation processes and present better perspectives for future researches.

Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activating of Peroxymonosulfate to Generate 1 O2 with 100 % Selectivity

Singlet oxygen (¹ O₂ ) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of ¹ O₂ . In this work, we develop a graphitic carbon nitride supported Fe single-atoms catalyst (Fe₁ /CN) containing highly uniform Fe-N₄ active sites with a high Fe loading of 11.2 wt %. The Fe₁ /CN achieves generation of 100 % ¹ O₂ by activating peroxymonosulfate (PMS), which shows an ultrahigh p-chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single-atom sites, the Fe-N₄ sites in Fe₁ /CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO₅ ^.- , and thereafter efficiently generate ¹ O₂ with 100 % selectivity. In addition, the Fe₁ /CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of ¹ O₂ for highly selective and efficient degradation of pollutants.